1. Field of the Invention
The present invention relates to a microscope apparatus provided with an immersion objective lens.
2. Description of the Related Art
Function analysis of genes is widely conducted through experiments on cultured cells; one of such experiments is performed by time-lapse observation in which cultured cells are intermittently photographed for a prolonged time period. The cultured cells, i.e., living cells are generally damaged by photostimulation. Hence, to minimize the damages to the living cells, an objective lens with a high numerical aperture (NA) is employed in the observation of the cultured cell because such a lens can capture more fluorescence with a smaller amount of exciting light.
Suitable objective lenses with a high NA for such observation are immersion objective lenses, which are employed together with high-refractive index liquid which fills up a space between the immersion objective lens and a sample to be observed. Japanese translation of PCT international application No. 2004-531765 proposes a liquid feeder which supplies liquid to the immersion objective lens. The proposed liquid feeder supplies liquid to the immersion objective lens through an outlet of a feeding unit arranged near a side of an exit lens of the immersion objective lens. Since the outlet of the feeding unit is located close to the exit lens of the immersion objective lens, a simply-structured liquid feeder can supply the liquid without the need of a moving mechanism for the feeding unit.
The above-described arrangement, however, in which the outlet of the feeding unit is located near the side of the exit lens, is disadvantageous in that a large amount of liquid is required for filling up a gap between the exit lens and the sample. The immersion objective lenses can be classified into two groups depending on the types of employed liquid; namely, the water immersion objective lenses that employ water and oil immersion objective lenses that employ oil. On the one hand, the use of the oil immersion tends to accompany increase in experiment cost, since the oil employed for the oil immersion is expensive, and a larger amount of oil needs to be supplied than is required simply for observation. On the other hand, the use of the water immersion also accompanies increase in experiment cost, since a container with a large capacity is required for storage of a larger amount of liquid than is necessary, and a high-performance pump needs to be provided for reduction of time required for the liquid feed.
A necessary amount of supplied liquid can be minimized with the use of a nozzle and a pump that are generally used for supply of determinate quantity of liquid. For the minimization of the amount of supplied liquid, however, the liquid must be fed from substantially directly above a targeted portion, i.e., the immersion objective lens. At a time of the observation, the nozzle has to be removed from a moving range of the immersion objective lens, and hence an additional mechanism for nozzle retraction and a driving unit for the mechanism are necessary, which implies a further increase in equipment cost.